1. Field Of The Invention
This invention relates generally to bicycles and drive sprocket gears and more particularly to a bicycle having a drive sprocket gear of a shape providing an abrupt change in gear ratio on change in pedal movement from a horizontal direction to a vertical direction.
2. Brief Description Of The Prior Art
Bicycles with a pedal driven sprocket gear driving a gear on the rear wheel were developed in the third quarter of the 19th century. In riding a bicycle, as the rider moves the pedals through a complete rotation, there are portions of the cycle of power application which are more effective than others.
In particular, when either of the pedals is at the top of its rotation and slightly forward of center, the cyclist can easily apply a strong downward force with considerable effect in the application of torque to the drive sprocket. On the other hand, when the pedal is pointed straight down, there is little or no torque being applied to the sprocket. Thus, during the vertical part of the movement, force is applied effectively, and during the horizontal part of the movement, there is little or no force applied.
During the last century, attempts were made to improve the gear relationships by making the drive sprocket gear elliptical in shape. This allegedly gave improved performance during certain portions of the operation of the drive sprocket. The use of elliptical drive sprocket gears has been suggested from time to time up to the present date. There are several patents which disclose various types of bicycles with elliptical or oblong gears.
Metz U.S. Pat. No. 513,589 discloses a bicycle with an elliptical drive sprocket gear.
Scovell U.S. Pat. No. 515,449 discloses a bicycle with an oblong drive sprocket gear.
Schaum et al U.S. Pat. No. 530,058 discloses a bicycle with an elliptical drive sprocket gear having means to compensate for variations in tension of the drive chain.
Delacroix U.S. Pat. No. 885,082 discloses another bicycle with an elliptical drive sprocket gear and means for compensating for slack in the drive chain during operation.
Hattan U.S. Pat. No. 3,259,398 discloses another bicycle with elliptical drive sprocket and having a system of idler gears for compensating for slack in the drive chain at different positions of operation.
Durham U.S. Pat. No. 3,899,932 discloses another elliptical drive gear with a special gear tooth design for preventing derailing of the drive chain.
Moretti Italian Patent 266,781 shows a bicycle gear system consisting of a drive sprocket, a driven gear for the rear wheel and an intermediate pinion gear. The drive sprocket has the appearance that it might have flat sides with curvatures at the apexes but an English translation reveals that continuous curves are all that is disclosed, e g., ovoid, helicoid, oval, etc., none of which have flat surfaces.
Frisiani Italian Patent 974,415 shows a bicycle gear system consisting of a drive sprocket, a driven gear for the rear wheel and an intermediate pinion gear. The drive sprocket is clearly elliptical and has no flat sides.
The present invention is distinguished over the prior art in that there is no previous disclosure of the use of drive sprocket gears having distinct rectilinear flat sections connected by circular sections which provide for an abrupt change in gear ratio at desired points in the movement of the sprocket gear. This invention is distinguished from the prior art in providing a bicycle having a rhomboidal (rhombus-like with circularly curved apexes) drive sprocket gear and a circular driven sprocket on the rear driven wheel. This gear arrangement varies the overall power input from the drive sprocket to the driven gear. The shape of the drive sprocket and the location of the drive pedal changes the gear ratio so that a low gear ratio is utilized during the horizontal portion of movement of the cyclist's legs and a high gear ratio is utilized during the vertical movement of the legs. The gear ratio with the rhomboidal (rhombus-like with circularly curved apexes) gear is constant during the horizontal part of the movement and abruptly changes at the approach to and during the vertical part of the movement of the cyclist's legs. While the rhomboidal (rhombus-like with circularly curved apexes) gear is shown primarily for bicycles it may be used in other systems for converting reciprocal to rotary movement with a change in gear ratio.